Current limiting fuse



Dec. 21, 1943. A. P. STROM CURRENT LIMITING FUSE Filed Sept. 19, 1940 R 0, m n w w m. 2 2 4 a n 4 m6 m Ad 4 4 v mFflfl A o e.Y

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and extinguish the resulting arc.

Patented Dec. 21, 1943 UNITED. STATES PATENT OFFICE asst-.504 I .Albert P. Strom, Forest Hills, r... assignor to Westinghouse Electric 8 Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 19, 1940, Serial No. 357,395

34 Claims. (01. zoo-1:0)

This invention relates generally to circuit interrupters, and more specifically .to interrupters which are capable of automatically interrupting the circuit in response to the passage therethrough of currents above a predetermined value. v and at the same time limit the value of the cur- Serial No. 357,393, filed September 19, 1940, and

assigned to the assignee of this invention.

The invention of the instant application is directed to improved constructions of a current limiting fuse, and one object of the invention is to provide a novel fuse which is capable of interrupting the circuit in a fraction of a half cycle, while limiting the current and volta e inter-.

rupted.

Another object of this invention'is to provide a novel arrangement of current limiting resistorfu'sion thereof, to obtain a very rapid transfer of the current to said current limiting means.

' A still further object of this invention is to provide a fuse of a novel design', having a novel and efliclentarrangement of parts rendering the fuse both. efllcient in operation, and economical to manufacture.

These .and other objects of this invention will mbecome'more apparent upon consideration of the a novel type of fuse having fusible means and :a

and shunt fuse to obtain a quick transfer of ourrent to the resistor when the fuse blows.

Another object of this inventionis to provide in a current limiting fuse of the type wherein current limiting means and fusible means are arranged in parallel circuit relation, additional fusible means arranged in series with said parallel 'circult for. interrupting the circuit in responseto currents above a predetermined value.

g Another object of this invention is to provide in a fuse having a fusible means, a novel arrangement of current limiting means, and are extinguishing means, to limit the current interrupted Another object of this invention is to provide a novel type of current limiting fuse utilizing a plurality of spaced current limiting elements, and

-- tube 2.

following detailed description of preferred embodiments thereof, taken in connection with the attached drawing, in which:

,Figure 1 is a central longitudinal cross-sectional view of a current limiting fuse embodying certain features of the invention.

Fig. 2 is a central longitudinal sectional view of a modified form of current limiting fuse.

Fig. '3 is a central longitudinal cross-sectional view of a still further modified form of current limiting fuse, and

Fig. 4 illustrates certain performance curves oi'a current limiting fuse constructed in accordance with this invention.

Referring to Figure 1 of the drawing, there is illustrated a fuse which includes an insulating fuse tube 2 .which may be of any desired insulating material such, for example, as fiber or synthetic resin. The fuse tube 2 is provided at opposite ends thereof with terminal caps l and 0, respectively, which are secured to the fuse tube 2 by having portions 8- and i0, respectively, punched inwardly to engage the material of fuse In the lower portion of the fuse tube 2 there is shown a substantially cylindrical current limiting member in the form of a resistor l2, which may be of any desired resistance material, preferably a carbon or carborundum rod or the like. This type of resistor, when. constructed of finely divided particles of carbon or other resistance material intimately .bonded together 'will have fusible means adapted to establish a plurality of arcs in series so as to transfer the current to said elements to thereby limit thecurrent, together with means for finally extinguishing the arcs and interrupting the circuit.

. Another object of this invention is to provide in a current limiting fuse havingcurrent limiting means and fusible means arranged in shunt relatlon, novel means cooperating with said fusible means for providing a high-arc voltage upon some .valve characteristics on high voltages due to breakdown and consequent discharge between particles and this feature is preferable for a purpose to be described. As shown, the resistor i2 is provided with a central bore ii, in which is received a tubular insulating sleeve it, which may be of any desired insulating material, such,

for example, as fiber. A fuse wire I8 is extended through the bore in insulating sleeve I B, and has one end thereof extended through a central aperture in terminal cap 6 to be bent over and soldered thereto as shown at i9. The other end of fuse wire it is soldered in an aperture 22, provided in a conducting, metal terminalpartition disk 20, located at the other end of resistor l2.

The bore through insulating sleeve l8 should be very small, and its minimum dimension is limited only by the size of fuse wire I 8 and in general should not be much greater in diameter than the diameter of the wire. The fuse wire I8 is preferablyconstructed of a materiaihaving a relatively high melting point and a high temperature coefficient, such, for example, as silver, for a purpose to be hereinafter described. The bore through insulating sleeve I8 needs to be quite small in order to restrict the are formed assasoa current value is reached which it is desired to limit. Accordingly, and by way of example, fuse wire 24 may melt in response to currents of one or ,two amperes, whereas fuse wire I 8 may not melt unless the current reaches a value of 80 when fuse wire l8 melts, to thereby provide a high are voltage, so that the current path may be quickly shifted to resistor l2, between terminal cap 6 and terminal disk 24. As stated above, the insulating sleeve l8 may be of any desired insulating material, although preferably of a material such as fiber which is capable of evolving an,-

arc extinguishing gas when in proximity to an electric arc, to thereby further aid in providing a high are voltage for an arc struck within insulating tube It. This is an important feature, because, in order to effectively limit the current,-

it is necessary that it be transferred to the resistor in a small fraction of a half cycle, after fuse wire 18 melts and before the cln'rent has had an-opportunity to build up to a high.value,and

before-the energy developed by the arc reaches a value which might cause damage to the fuse.

In the-upper portion of the fuse tube 2, as seen in Fig. 1, there-is provided a fuse'wire 24, having one end secured in. aperture 22 of terminal disk 20, as by soldering or the like, and the other end thereof is secured to terminal cap 4 in a like manner. The fuse wire 24 is preferably of a-material which will melt on lower currents than fuse wire it and may, for example, beof a lead-tin alloy. Spaced along the length of fuse wire 24, there are provided blocks 26,- of a material which is capable of evolving an arc extinguishinggas when in proximity to an electric arc, such, for example, as boric acid,

' gypsum, or asynthetic resin. As shown, these blocks 28 are provided with substantially central bores 28 therethrough, which are substantially larger than fuse 'wire 24, and insulating spacer sleeves 30 are provided between blocks 26 to maintain the blocks in spaced relation. The spacing sleeves 20 may be of any desired insulating material, such for example, as fiber or the like.

'The circuitthrough the fuse shownin Fig. 1 may now be traced from. terminal cap, 4, fuse wire 24, to terminal disk'i l, and thencein parallel paths, one of which extends l'through fuse wire I 8 to terminal cap 8, and the other of which extends through resistor l2 to terminal cap 8. Obviously, under normal load conditions all of the current passing through the fuse will flow through fuse wire 24, and the major portion of the current will continue through fuse wire l8 to terminal cap 8. Only a relatively minor portion of the current, if any, will normally flow through resistor I 2.

' sulating sleeve l8, and because of the high are voltage obtained in the manner described above,

the current flow will be transferred within a fraction of a half cycle to resistor I 2 which will thereby limit the current, and this limited cur amperes. It follows fromthis example that on currents below the value of currents which itis desired to limit, that is, in the example given, 80 amperes, fuse wire l8 may not melt and the current will be interrupted easily within the upper end of the fuse as shown in Fig. 1 by the action of un-ionized gases evolved from blocks 26.

When resistor l2 also has a valve characteristic, this feature is made use of to limit the maximum voltage across the fuse to a safe value which may be, for example, about twice normal line voltage. Upon the occurrence of a short circuit having exceptionally ,high current, the arc voltage in bore 14 might go above this safe value, unless a resistor is employed which decreases in resistance at said safe high voltage. The valve eifect of the resistor therefore, should operate to reduce the resistance thereof at a predetermined high voltage, which may be, as in the above example, about twice line voltage.

A modified form of the, invention is illustrated tained in spaced relation along fuse tube 2 by insulating spacer sleeves 34 positioned between the blocks, and which may be of any desired insulating material, such, for example, as fiber or the like. Within each spacer sleeve 34 there is provided are extinguishing material 38 which may be in the form of a powder of inert material, but preferably is material which is capable of evolving an arc extinguishing gas when in proximity to an electric arc, like the material comprising blocks 28 in the embodiment of the invention shown in Fig. 1, only in powder form. Ob-

viously, arc extinguishing material in solid block form with' quite large bores therethrough, so as not to confine fuse wire 40, like blocks 28 of Fig. 1, may be used if desired.

As shown, each resistor block 32 is provided with a small substantially central bore 38,

through which is threaded a fusible wire 40,-

secured at one end to terminal can 4, as by solder- .ing or the like, and having the other end thereof extended through an aperture in end cap 8 to 'be bent over and secured .to the cap as at 42.

Fuse wire 40 may be of any desired fusible material having a relatively low melting point such,

for example, as a lead-tin alloy. It will be noted that the fuse wire 40 extends through relatively small openings in resistor blocks 32 similar to the opening in resistorblock l2 for fuse wire iii species shown in positioned in the lower part of resistor rod may be of the same material as re-. sistors l2 and 32 previously described. A fuse, wire 46 preferably of a material similar to the fuse in the embodiment of the invention shown in Fi 1.

In operation, when an overload appears in the circuit, fuse wire 40 is first melted within one or more of the passages 38 through resistor blocks 32, because in these passages the fuse wire is confined by solid walls, and accordingly, there is less dissipation of heat from the portions of fuse wire 40 within bores 38 than from the portions of the fuse wire between resistor blocks. Wire 40, having fused in one or more of passages 38 to form an arc, which will have a high arc voltage since it is restricted to the small passages 36, will cause the arc current to be substantially instantaneously transferred through adjacent resistor blocks 32. As soon as current passes through one or more resistor blocks 32, these obviously will function to limit the current, and the current thus limited will be easily interrupted by the arc extinguishing material 36. be-

tween resistor blocks 32. In connection with this embodiment of the invention it will be noted that on high currents a plurality of arcs will be formed in series which may produce a still higher arc voltage than would be possible if but a single arc were formed. In other .words, the sum of the arc voltages of a plurality of series 'arcs may be greater than the arc voltage for a single arc.

This obviously will promote still quicker transfer of the currentto the resistor elements.'and limit the current at an earlier point in its ascending curve. 1 Although but a single fuse wire is shown in connection with this embodiment of the invention. it is obviousthat different fuse wires may be provided in restricted bores 36 than in the spaces outside resistors 32, in the manner disclosed in connection with Fig. 1.

- Referring now to Fig: 3 of the drawing, a still further embodiment of the invention is shown,

and inasmuch as many of the'parts illustrated in this embodiment of the invention are identical with those illustrated in connection with'the numerals will be used to designate like parts.

In Fig. 3 there is shown a solid resistor rod 44 the fuse, and this wire l8, described in connection with the embodiment of the invention shown in Fig. '1. is wrapped around resistor rod 44 in substantially aspiral fashion, and has one, end thereof extended .through an aperture in terminal cap 6 and bent over to be secured thereto as at 48, and the other end thereof is securedin an aperture 50, in a.

conducting, metal terminal partition disk 52 pcsitioned at the opposite end of resistor, rod 44. The end of fuse wire 46 may be secured in aperture 50 in any desired manner, 'such. for example, as by soldering or the like. Fuse wire 46 is preferably closely surrounded by walls of insulating material, and may even be embedded in insulating material 54 as shown on the drawing. Although good results have been obtained by using enameled wire, for example, and covering this with one or more layers of cellulose acetate tape or a tape impregnated with water-glass, it is preferred that the fuse wire 46 be entirely embedded in an insulation material which may be in the form of a plastic, such as a viscous paint made of a solution of cellulose acetate, or ethyl cellulose, or synthetic resin or the like, which is capable of evolving an arc extinguishing gas when in proximity to an electric arc. The purpose of embedding the fuse wire 46 in such a material, is to provide a very small arc passage when the fuse wire melts, to thereby obtain a high are voltage to quickly transfer the current to resistor rod 44. Obviously, if insulating material 54 is of .the gas evolving type, the arc voltage will be higher than if the insulation 54 is of an inert type. Positioned above terminal partition disk 52, as shown in Fig. 3, there is provideda lining 56 for the fuse tube 2 which is preferably of a gas evolving material like the blocks 26 described in connection with Fig. 1. The gas evolving material 56 is provided with a bore 58 therethrough, for receiving afuse wire 60 which is secured between terminal disk 52 and end cap 4, ii -any I desired manner, such, for example, as by soldering or the like, and is of a material like fuse wire 24 previously described, which melts on lower currents than fuse wire 46.

The electrical circuit through the fuse shown in Fig. 3 is similar to that described in connection,

rent, and the main current path through the fuse Figs. 1 and 2, like reference will be from end cap 4, through fuse wire 66, ter-- minal disk 52, and fuse-wire 46 to endcap' 6.

, Upon the occurrence of a short circuit, fuse wire which is of a different material, and has different characteristics than fuse wire 46, and is preferably of a material. like. that of fuse wire 24,

' described in connection with Fig. 1 of the drawing, will melt and substantially instantaneously thereafter fuse wire 46 will also melt to establish an arc in the very small bore in insulating materlal 54. It willbe' noted that not only is this bore extremely small, but that it is also quite long due to the coiled arrangement of-fuse wire 46, and'this also helps to provide an extremely high are voltage, so that the current will be'suba stantially instantaneously shifted to resistor rod 4 4, to thereby limit the current, and'permit the current as thus limited to be interrupted within bore 58 through gas evolving material 56. It will be noted that the operation of the fuse shown in Fig. 3 is much like that of the fuse shown in Fig. l, and therefore will notbe described again in detail to avoid repetition. However, certain features of the fuse shown in Fig. 3 are important,-

especially the; feature which enables the 'use of a longer parallel fuse wire to thereby attain a desirable high are voltage when this fuse wire melts, to obtain quick transfer of the current to tliecurrent limiting resistor element.

All three of the embodiments of the invention disclosed have the advantage that with these constructions a relatively large resistor may be ,employed, since, as shown, the resistor may occupy substantially one-half the total space within the fuse tube. This results in a larger current carrying capacity without excessive heating. Also the overall length of the fuse may be reduced. because, with the constructions disclosed herein, portions of the fuse elements may be passed through or parallel to the resistor elements, and this is of advantage with these constructions of current limiting fuses since it is highly desirable to locate such portions of-fuse elements in very small passages, to restrict the are formed when they blow.,' All three embodiments of the inventicn also utilize current limiting resistor elements the fuse blows, especially on currents above predetermined values for limiting the maximum value of such currents.

In Fig. 4 of thedrawing there is illustrated typical voltage and current curves plotted with respect to time, and which provide a graphic example of the performance of a fuse constructed in accordance with this invention. In Fig. 4, the

dotted line curve designates the normal short circuit current if it were not limited. Curve V designates the circuit voltage, point A designates the point at which the fuse blows, curve I: designates the current as limited by applicant's fuse, curve Vr indicates the voltage across the fuse, and point B indicates the time'when interruption occurs.

It will beobvious' upon consideration of these- -curves that circuit interruption occurs within a fraction of a half cycle after the fuse blows, or a predetermined time after the current reaches a value predetermined by the size of the fuse wire employed, and the current is limited as soon as the parallel fuse wire melts to a very small fraction of the normal short circuit current, and even the voltage across'the fuse is not much higher than line voltage. As the system short circuit capacity increases, the time at which current limitation occurs also decreases, as does the ratio of the limited current to the system capacity, because the current will be shifted to Y the resistor at an earlier point. The reason for the relatively low voltage across applicant's fuse -is that although a high arc voltage may result from the arc structure in insulating tube It of Fig. 1, resistor bores 38 of Fig. 2 or insulating material 54 of Fig. 3, this causes transfer of the current to the. resistors, and the voltage can rise only to a value high enough to transfer all of the current to the resistors, and this occurs in a very few microseconds. Of course, the size and charassjmoc tion. while being relatively small and compactin construction. and economical to manufacture.

Although the-resistance elements in each of the embodiments of this invention arereferred to herein and in the claims as "current limiting means," it is apparent that the high arc voltage, which occurs instantaneously upon fusion of the fusible element shunting each resistance element, will limit the rise of current prior to its transfer to the resistance element, and thus exert an initial current limiting effect. The resistance element is effective as soon as transfer of the current to it occurs, to limit the current to a predetermined value, and this current is then finally interrupted by the series fuse element at the first current zero. The instantaneous transfer of current to the resistance element will, obviously, also limit the voltage to a value determined by the current flowing through the resistance element, and this action is enhanced by the-use of a resistance element-having valve characteristics, as

. previously described.

acteristics of the parallel fuse wire accounts for the low peak in the I: curve, and since the fuse has only tointerrupt a current which is limited by the resistor means, interruption is quickly accomplished in a small period of time as illustrated by way of example in Fig. 4. .The.time for interruption of the circuit is decreased materially in a fuse of this type, due to the fact that the current after transfer to the resistor is at almost unity powerfactor, thereby advancing current zero so that-interruption occurs in a small fraction of a half-cycle.

' Where the word instantaneously" or term "at the same instant? is used herein and in the claims to denote a time of operation, this means I a time of less than a half cycle of a 60 cycle wave,

and preferably in a small fraction of a half cycle 1 the order of a few hundred micro-seconds.

In the foregoing there has been specifically disclosed various embodiments ofan invention specifically relating to current limiting fuses wherein a fuse wire is provided paralleling a resistor element, with both electrically and mechanically related in various novel combinations, and further arranged in conjunction with are extinguishing means, to provide a current limiting fuse which is-particularly eiiicient in operait is'desired that the invention be not limited to the particular embodiments specifically disclosed herein, inasmuch as it will be obvious, particularly to persons skilled in the art, that many changes and modifications may be made in'these particular structures without departing from the broad spirit and scope of this invention. Therefore it is desired that the invention be interpreted as broadly as possible and that it be limited only by the prior art and by what is expressly set forth in the following claims.

I claim as my invention:

1. In a circuit interrupter, current limiting means, means for automatically establishing an arc in response to currents above a predetermined value arranged in shunt relation with respect to said current limiting means, means positioned to act on saidarc to, provide an arc voltage of a predetermined value which is greater than the voltage drop through said current limiting means same instant the arc is struck to cause instantaneous transfer of the current to said current limiting means, and means for automatically interrupting the circuit in response to currents above a predetermined value and connected in series with said current limiting means and arc establishing means.- I

2. In a current limiting 'fuse device, current limiting means having a passage substantially coextensive with said current limiting means,

fusible means in said passage and arranged in shunt relation with respect to said current limiting means.

3. In a circuit interrupter, current limiting I means, means for. automatically establishing an arc in response to currents above a predetermined value, means positioned to cause-the arc voltage to rise to said predeter-. I

mined'value at the same instant the arc is struck,

said are establishing means being associated with said current limiting to act on an arc estab lished by said are establishing means to provide an arc voltage of a predetermined valuewhich is means in such a manner.

2,387,504 that said instantaneous arc voltage causes instantaneous transfer of'the current to said current limiting means, and means for automatically interrupting the circuit in response to currents above a'predetermined value and arranged in series circuit relation with said current limiting means and are establishing means at least duringa current limiting operation.

4. In a circuit interrupter, current limiting means, means for automatically establishing an arc in response to currents above a predetermined value arranged in shunt relation with respect to said current limiting means, solid means of in,- sulating material positioned to restrict said are to provide an arc voltage of a. predetermined value which is greater than the voltage drop through said current limiting means for any instantaneous value of current flowing in the circuit, said means acting on the arc'being constructed and arranged to cause the arc voltage to rise to said predetermined value at the same instant the arc is struck, said arc establishing means being associated with said current limiting means in such a manner that said instantaneous arc "voltage causes instantaneous transfer of the current to said current limiting means, and means for automatically interrupting the circuit in response to currents above a predeter- .mined value and connected in series-with said thereto of a. material capable of evolving an arc extinguishing gas when in proximity to an elec-' tric arc.

5. In a circuit interrupter, current limiting means, means for automatically establishing an arc in response to currents above a predetermined value arranged in shunt relation with respect to said current limiting means, solid means of in-- sulating material capable of evolving an are ex-' tinguishing gas when in proximity to an electric ing means, and additional fusible means located outside said passage and arranged in series rela- .tion with respect to said current limiting means and fusible means in said passage.

8. In a fuse, a fuse tube having insulated terminals adjacent opposite ends thereof, current limiting resistor means in said tube and occupying a substantial portion but not all of the space along said tube with one end of said resistor means electrically engaged with one of said terminals, and fusible means connected between said terminals and including fusible portions ex tending along said resistor means and across at least certain of the spaces between said ,resistor means;

10. In a fuse, a fuse tube having insulated terminais adjacent opposite ends thereof, spaced current limiting resistor means in said tube and occupying a substantialportion of the space in said tube, fusible means connected between said terminals and including fusible portions extending along said resistor means andacross at least are forming a narrow passage for restricting an are established by said are establishing means to provide an arc voltage of a predetermined value which is greater than the voltage drop through said current limiting means for'any instantaneous value of current flowing in the circuit, said means acting on the are being constructed and arranged to cause the arc voltage to rise to said predetermined value at the same instant the arc' is struck, said are establishing means being associated with said current limiting means in such a manner that said instantaneous arc voltage causes instantaneous transfer of the current to said current limiting means, and means for auto matically interrupting the circuit in response to currents above a predetermined value and connected in. series with said current limiting means and are establishing means.

tinguishing means arranged in cooperative rela-- tion at least with the portion of said fusible means located outside said passage.

7. In a current limiting fuse device, current limiting means having a passage substantially coextensive with said current limiting means, fusible means in said passage and arranged in shunt relation with respect to said current limitcertain of the spaces between said resistor means, and are extinguishing means located in at least said certain of said spaces between said resistor means.

11. In a fuse, current limiting resistor means having a, bore therethrough, and fusible means in said bore and connected in parallel circuit relation with said resistor means.

12. In a fuse, current limiting resistor means having a bore therethrough, fusible means in said bore and connected in parallel circuit relation with said resistor means, and additional fusible means outside said bore and connected in series with said parallel circuit.

13. In a fuse, current limiting resistor means having a bore therethrough, fusible means in said bore and connected in parallel circuit relation with said resistor means, and said bore being Y of a size to restrict the are formed upon fusion of said fusible means to thereby create a high arc voltage and cause rapid transfer of the current to said resistormeans.

14. In a fuse, a fusetube having insulated terminals adjacent opposite ends thereof,-current limiting resistor means in said tube and occupy'-= ing asubstantial portion of the space in said tube with one end of said resistor means electrically engaged with one of said terminals, a

fuse wire connected between said terminals and having a portion thereof extending along said resistor means, and said portion of said fuse wire being closely surrounded by insulating material to provide a small bore for the are formed when said fuse wire melts.

15. In a fuse, a fuse tube having insulated ter- "minals adjacent opposite ends thereof, current resistor means. and said portion of said fuse wire being closely surrounded by insulating material which is capable of evolving an arc extinguishing gas when in proximity to an electric arc to provide a small bore for the arc formed when said fuse wire melts.

16. In a fuse, a fuse tube having insulated terminals adjacent opposite ends thereof, current limiting resistor mean in said tube and occupying a substantial portion of the space in said tube with one end of said resistor means elec-.

trically engaged with one of said terminals, a fuse wire connected in shunt relation with said resistor means and closely urrounded by means of insulating material to form a restricted arc passage, and anotherfuse wire connecting said resistor to said other terminal and having a lower melting point than said first mentioned fuse wire. 17. In a fuse, current limiting resistor means, and a fuse wire substantially spirally wound about said resistor means and connected in shunt relation with said resistor means.

.18. In a fuse, current limiting resistor means,

. a fusewire substantially spirally wound about said resistor means and closely confined in a passage of substantially the sam cross-section as said wire, and said wire being connected in shunt relation-with said resistor means.

19.. In a fuseficurrent limiting resistor means, a fuse wire substantially sphally wound about said-,resistor means and closely confined in a passage of substantially the same cross-section as said wire, said wire being connected in shunt relation with said resistor means, and at least inner wall portions of said passage comprising a material which is capable of evolving an arc extinguishing gas when in proximity to an electric arc.

20. In a fuse, a fuse tube having insulated terminals adjacent opposite ends thereof, current limiting resistor means in said tube and occupying a substantial portion of the space in said tube with one end of said resistor means electrically engaged with one of said terminals, and

, fusible means coiled about said resistor and connected in shunt relation therewith, and additional fusible means connecting said resistor means to the other of said terminals.

21. In a .use, a fuse tube having insulated terminals adjacent opposite ends thereof, partition means including terminal means dividing said tube into at least two compartments, currentlimiting means, and a, closely confined shunt fusible means in one of said compartments and connected between said terminal means and one of 55 said terminals, and a second fusible means having diflerent characteristics located in another of -said compartments and connecting said terminal means and the other or said terminals.

22. In a circuit interrupter, means for establishing an arc, means cooperating with said are to provide an instantaneous high arc voltage,'and

I current limiting means, the resistance of which decreases when subjected to voltages above a predetermined value arranged in shunt relation with to said arc establishing means for limiting the current and voltage.

23. In a circuit interrupter, current limiting valve means, are establishing means in shunt ire-=- lation with said current limiting means, means cooperating with an arc established by said are establishing. means to substantially instantm,

neously raise the arc voltage thereof to a value above that necessary to transfer the current to said current limiting means, and said current limiting means being responsive to voltages above said value to reduce its current limiting effect and thereby limit such voltages;

24. In a fuse, a resistor block, a fuse wire spirally wound about said resistor means and connected in shunt relation with said block, and insulating means between said wire and resistor means.

25. In a fuse, a fuse tube having insulated ter- 10 minals adjacent opposite ends thereof, closed partition meansincluding terminal means dividing said tube into at least two compartments, current hunting means and a closely confined shunt fusible means in one of said compartments and connected between said terminal means and one of said terminals, and a second fusible means having different characteristics located in another of said compartments and connecting said terminal means and the other of said terminals.

28. In a fuse, a fuse tube having insulated terminals adjacent opposite ends thereof, transverse partition means dividing said tube into a plurality of compartments, current limiting means and shunt fusible means in one of said compartments and connected to the adjacent terminal, series fusible means in another of said compart ments and connetced to the other of said terminals, and connections extending through and sealed in said partition means for connecting said go fusible means and current limiting means.

27. In a fuse, a fuse tube having'insulated terminals adjacent opposite ends thereof, current limiting resistor means in said tube and occupying a substantial portion of the space in said tube with one end of said resistor means electrically engaged with one of said terminals, fusible means connected between said terminals and having a fusible portion thereof extending along said resistor means, and said portion of said 40 fusible means being closely surrounded by insulating material to provide a small bore for the are formed when said fusible portion melts.

28. In a fuse, a fuse tube having insulated terminals adjacent opposite ends thereof, current limiting resistor means in said tube and occupyingv a substantial portion of the space in said tube with one end oi! said resistor means electrically engaged with oneof said terminals, a fuse wire connected in shunt relation with said resistor means and closely surrounded by means of insulating material to form a restricted arc passage, another fuse wire connecting said resistor to said other terminal, and means of a material capable of evolving an arc-extinguishing gas occupying substantially all of the remaining space in said tube and forming an arc passage for said other fuse wire.

29. In a fuse, current limiting means and fusible means connected in shunt relation, means for restricting the arc formed upon fusion of said fusible means to provide an instantaneous high are voltage, and one of said first two mentioned means being in the form of an elongated strip of material spirally arranged about the other.

30. In a fuse, current limiting means and fusible means connected in shunt relation, and-one of said means being in the form of an elongated 7 strip of material spirally arranged about the other. I v

31. In a fuse, current limiting means and fusible means connected in shunt relation, one of said means being in the form of an elongated to strip of material spirally arranged about the other, and insulating means between said first two mentioned means.

32. In a circuitlinterrupter, current limiting means, fusible means, means positioned to act on the are formed upon fusion of said fusible means to provide an arc voltage of a predetermined value which is greater than the voltage drop throughsaid current limiting means for any instantaneous value of current flowing .in the circuit, said means acting on the are being constructed and arranged to cause the arc voltage to rise to, said predetermined value at the same instant the arc is struck, said fusible means associated with said currentlimiting means in such a manner. that said instantaneous arc voltage 4 causes instantaneous transfer of the current to said current limiting means, and a second fusible means connected in series with said firstmentioned fusible means.

' a 33. In a circuit interrupter, current limiting means, fusible means, means positioned to act on the are formed upon fusion of said fusible means to provide an arc voltage at the instantsaid arc is struck which is greater than the voltage drop through said current limiting means for any instantaneous value of current flowing in the circuit, said fusible means associated with said current limiting means in such a manner that said instantaneous arc .voltage causes instantaneous transfer of the current to said current limitingv means, and a second fusible means having a lower melting point than said first-mentioned fusible means and connected in series with said first-mentioned fusible means.

34. In a circuit interrupter, resistance means. means forautomatically establishing an arc in response to currents above a predetermined value,

resistance means in sucha manner that said instantaneous arc voltage causes instantaneous transfer of the current to said resistance means, and means for automatically interrupting the circuit in response to currents above a predetermined value and arranged in series circuit relation with said resistance means and are establishing means at least during a current limiting operation.

ALBERT P. STROM. 

